My invention relates to slow wave circuits and, more particularly, to slow wave circuits useful as component elements of traveling wave tubes and other microwave frequency apparatus.
Certain high frequency microwave devices useful in the microwave frequency spectrum employ as an element a circuit device variously known in the art as a traveling wave circuit or slow wave structure. Common and well known devices of that type include the O-type traveling wave tube and phase shifters. As is known to those skilled in the art, there exists a large number of slow wave circuits or structures or various types and geometries having various electrical characteristics that differ from one another in known ways. Two slow wave structures that are widely known and used are the ring loop and the helix. One purpose of the slow wave structure is to reduce the propagation velocity of a signal of the microwave frequency spectrum to a lower velocity from the normal propagation velocity theoretically approximating the speed of light. By way of example, the microwave signal applied to one end of an elongated spiral helix propagates around the turns of the helix at the speed of light but in effect propagates along the axis of the helix at an effectively lower velocity than the speed of light, the exact velocity being dependent upon the number of turns per unit of axial length of the axis in the helix and the helix diameter. Other examples of slow wave structures are illustrated in patents U.S. Pat. No. 3,287,668 to Veith et al, U.S. Pat. No. 3,273,081 to Itzkan, U.S. Pat. No. 2,957,103 to Birdsall, U.S. Pat. No. 3,230,485 to Sobotka, U.S. Pat. No. 3,508,108 to Salisbury, U.S. Pat. No. 3,413,512 to Buck, U.S. Pat. No. 3,050,657 to Branch, U.S. Pat. No. 1,945,544 to Conklin, U.S. Pat. No. 3,639,860 to Breitenbach, which have been made known to me, and in Traveling Wave Tubes Theory and Application, published 1971, Litton Precision Products, Inc. And a ring loop circuit is presented in my prior patent U.S. Pat. No. 3,716,745. Many of the aforecited references illustrate the slow wave structure as an element of the conventional O-type traveling wave tube.
The traveling wave tube is a microwave frequency device used primarily as an amplifier of microwave frequency signals. The tube operates on the physical phenomenon of an electronic interaction that occurs between electrons moving by a slow wave circuit and a microwave signal propagating along the slow wave circuit. By means of this interaction, kinetic energy in the electrons is converted into power in the microwave frequency signal. In its essentials the traveling wave tube includes a source of electrons, a slow wave structure enclosing an interaction region, a collector located at the end of the interaction region, an input coupling to one end of the slow wave structure for coupling of microwave frequency source to the slow wave structure and an output coupling located at the other end of the slow wave structure for coupling out amplified microwave frequency signals. The aforecited elements are contained in an envelope maintained in high vacuum. The exact details of construction, additional elements and operation of such prior art devices in which the present invention is to be incorporated as an element is described in the prior art literature, including the cited patents, known to those skilled in the art, to which the reader may make reference. Several electrical characteristics of interest in a slow wave structure include frequency bandwidth, efficiency, gain per unit wavelength, harmonic power generation, dispersiveness, interaction velocity, interaction impedance, and .omega.-.beta. characteristic.
The present invention relates to a slow wave structure as an element of a microwave frequency apparatus, such as a traveling wave tube, and to a novel configuration of a conductor formed in a microwave apparatus combination as a path for electromagnetic energy in the microwave frequency range possessing certain desirable electrical characteristics and obtaining certain desired results.